Helical bar printer and hammer therefor

ABSTRACT

In a printer which selectively prints in response to binary coded input character signals, a plurality of rigidly supported, lightweight blades repeatedly strike a continuously rotating helical bar, printing dot patterns. A movable, lightweight coil fixed to each blade respectively and disposed in a magnetic field drives the blade. Logic circuits, which control the hammers to print alphanumeric characters, include a read only memory which stores binary signal sets representing dot patterns to be printed in rows to compose alphanumeric characters. In response to the received binary characters, addresses in the read only memory are selected to compose the corresponding alphanumeric characters. The binary signal sets at the selected addresses are read out to shift registers, one corresponding to each hammer. The signals in the shift register are read serially out of the shift registers and control actuation of the corresponding hammers as they are read out.

United States Patent [191 Potter HELICAL BAR PRINTER AND HAMMER THEREFOR [75] Inventor: John T. Potter, Locust Valley, NY. [73] Assignee: Potter Instrument Company, Inc.,

Plainesview, N.Y.

[22] Filed: May 21, 1970 [21] Appl. No.: 39,314

[52] US. Cl. 101/93 C, 197/1 R, 346/101 [51] Int. Cl B41j 7/08 [58] Field of Search 101/93 C; 197/1; 178/5,

[56] References Cited UNITED STATES PATENTS 2,909,996 10/1959 Fitch 101/93 C 3,072,045 l/l963 Goin 101/93 C 3,112,358 ll/l963 Veno 178/5 3,138,427 6/1964 Stein et al..... 346/101 3,138,429 6/1964 Cooley 346/101 3,159,710 12/1964 Sorgi 346/101 X 3,279,362 10/1966 Helms 101/93 C 3,286,625 11/1966 Petit l0l/93 3,409,904 ll/l968 Maiershofer 346/101 3,478,289 ll/l969 Parnell 335/231 [111 3,834,304 [451 Sept. 10, 1974 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Edward M. Coven [5 7] ABSTRACT In aprinter which selectively prints in response to binary coded input character signals, a plurality of rigidly supported, lightweight blades repeatedly strike a continuously rotating helical bar, printing dot patterns. A movable, lightweight coil fixed to each blade respectively and disposed in a magnetic field drives the blade. Logic circuits, which control the hammers to print alphanumeric characters, include a read only memory which stores binary signal sets representing dot patterns to be printed in rows to compose alphanumeric characters. In response to the received binary characters, addresses in the read only memory are selected to compose the corresponding alphanumeric characters. The binary signal sets at the selected addresses are read out to shift registers, one corresponding to each hammer. The signals in the shift register are read serially out of the shift registers and control actuation of the corresponding hammers as they are read out.

8 Claims, 5 Drawing Figures PAIENTEDSEPI 0 3.884.304

' sum 1 or a INVENTOR F/ G. 3. I JOHN POTTER r MW).

OR N15 to" BACKGROUND OF THE INVENTION This invention relates to printers and more particularly to a printer which prints in response to coded input signals such as would be used to print the output from data processing equipment or computers.

Prior to the present invention, it has been proposed to print by means of a rotating helical bar which is struck by an impact hammer such as a blade. Each time a blade is actuated it strikes against the rotating helical bar and prints a dot. If the blades are controlled to strike at the proper times as the helical bar rotates, the printed dots can be arranged in patterns to compose any desired information such as alphanumeric characters, for example. This type of printer, referred to as a helical bar printer, was first used in facsimile printing, and then later it was used to. print selected alphanumeric characters in response to the coded input signals.

Helical bar printers are relatively inexpensive and simple as compared with other impact printers capable of producing multiple copies. Although proposals have been made to use a separate helix and separate hammer for each seven or eight columns, usually one helix and one hammer blade serve to print an entire line. However, in a helical bar printer for printing alphanumeric characters, the blade must be able to strike in about 35 positions for each character in order to get good character definition. Because of difficulty in achieving the very high hammer firing rates required, helical bar printers of the prior art print at a very slow line rate.

The present invention, because of its improved logic system for controlling the printer to print the proper patterns of dots to compose the alphanumericcha'racters and because of an improved hammer construction, is many times faster than the selective helical bar printers of the prior art.

SUMMARY OF THE INVENTION In accordance with the present invention as in the printers of the prior art, a helical bar is continuously rotated and is struck by an impact hammer.,Preferably, each helix and its associated hammer spans on the order of l 1 character positions along the print line, and the hammers are actuated in parallel in order to in crease the speed at which a line is printed.

Binary signals representing an entire line of alphanumeric characters to be printed are stored in a register. These characters are fed in sequence to a read-onlymemory and then binary signals representing dot patternsto be printed in a horizontal row are read out in parallel to shift registers, there being one shift register for each hammer. The signals representing the dot patterns are then shifted out of the shiftregisters and control the actuation of the hammers which will print the dot patterns along. a single row for each revolution of the helix. The signals representing each row dot pattern are fed in parallel to the shift registers during the time that the intersections of the helical bar and the hammer blades are passing through the spaces between characters. In this manner no time is lost waiting for the shift registers to be filled with the dot patterns.

Each hammer blade is fixed to a lightweight coil of wire which is positioned in a narrow, uniform magnetic gap. The blade is mounted on a rigid, lightweight frame which can pivot through a small arc toward the helix. A hammer firing pulse is applied to the coil; the coil moves a short distance in the magnetic field and drives 5 the blade at a high speed against the helical bar, thus causing a dot to be printed.

Because of the extremely low inertia hammer system, the hammers can be actuated and returned into position ready to be actuated again in a very short interval 10 of time, permitting alphanumeric characters to be printed at a high speed.

Further advantages of the present invention will become readily apparent as the following detailed description of the preferred embodiment of the invention 1 5 unfolds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates the arrangement of the helical bar and hammers of a printer of the present invention.

FIG. 2 is a view in elevation of a hammer of the present invention.

FIG. 3 is a sectional view taken along the lines 3--3 of FIG. 2 and also showing in section a drum on which a helical bar is mounted.

FIG. 4 is a block diagram illustrating a logic system for controlling actuation of the hammers of the printer of the present invention.

FIG. 5 is a block diagram illustrating the details of the logic system of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, in a printer of the present invention a drum 11 is driven continuously at a high speed by a motor 12 in close proximity to a row of print hammers l5 aligned along a line parallel to the axis of the drum. A helical bar 13 on the cylindrical surface of the drum 11 extends around the drum in one complete convolution fo each hammer 15. In a preferred embodiment of the invention, each hammer l5 spans l l character positions along the print line; a l32-column printer has 12) print hammers. It should be noted that because there is a convolution of bar 13 for each hammer, as the drum 11 rotates, the helical bar 13 is in the same dot printing position with respect to each hammer. For example, when the bar 13 is in the third dot printing position from the left-hand edge of the left most hammer 15, it is in the third dot printing position with respect to each hammer. A so-called tone wheel on the drum 11 may be used to generate a series of electrical pulse signals indicative of the angular position of the helix. In this manner the hammers can be conveniently fired simultaneously in order to increase the line printing speed.

Each of the hammers 15 comprises a blade 17 positioned so that the edge 10 of the blade will strike the helical bar 13 when the hammer is actuated. Each 0 blade 17 spans only one convolution of the helical bar a hammer is actuated, a hammer blade 17 moves toward the helical bar 13 and a small, generally rectangular dot defined by the intersection of the hammer blade and the helical bar is printed on the paper web 19.

The paper web 19 is moved continuously in the direction indicated by the arrow in FIG. 3 by means of a suitable paper feed mechanism well known in the art (not shown). Alternatively, the paper may be driven intermittently, if desired, stopping while each horizontal row of data is printed. The ribbon 20 may be similar to a typewritter ribbon and is driven continuously between the hammers and the paper web 19 in a direction perpendicular to the direction of paper travel by suitable means known in the art. The hammers 15 are actuated at a high rate to print clots in a pattern, one horizontal row at a time, forming lines of alphanumeric characters as the paper web 19 advances past the hammer blades.

If the paper is driven continuously as the characters are printed, the row of characters printed by each hammer would be slightly skewed with respect to the direction of paper movement if each hammer blade were precisely positioned in the plane of the axis of the drum 11. To prevent the skewing of the printed characters and to maintain the characterrows perpendicular to the direction of paper travel, the plane of each hammer k blade 17 can be slightly skewed with respect to the axis of the drum 11.

Each character position, defined as an area on th web 19 in which an alphanumeric character can be printed, is preferably made up of X7 rectangular field of 35 dot positions. Of course, character fields of more or less than 35 dots can be employed, if desired. Each of the hammers can be actuated to strike its blade 17 against the helical bar 13 in any selected pattern of dot positions in each of the character fields and in this manner compose any selected alphanumeric characters in each character position.

FIGS. 2 and 3 show one hammer in detail; the blade 17 is fixed to a lightweight, rigid frame 23. A pair of pins pivotally mount the frame 23 in a U-shaped bracket 27 which allows the blade to pivot toward and away from the helix bar 13.

The blade 17 is cemented by means of an epoxy to a thin circular ring 31 which, in turn, is cemented to a coil 33 of fine wire wound on a lightweight, cylindrical support member 34. The annular coil 33, which serves as the hammer drive coil, is supported by frame 23 in an air gap 36 between a cylindrical core and a circular pole piece 37. One pole of a permanent magnet abuts the core 35 and its other pole is magnetically cou- 'pled to the pole piece 37 by means of soft iron pieces any suitable manner known in the art such as screws or epoxy, care being taken not to leave any gaps between the members. The hammers l5 are secured to a suitable structural frame 51 (shown schematically). Preferably, there is a resilient mounting pad 52 between the frame and the hammers in order to prevent vibrations from being transmitted among the hammers. Conveniently, the U-shaped bracket 27 is bolted to the pole piece 37.

The magnetic flux circuit can be traced from the right hand pole of magnet 45 through the core 35, through the narrow annular gap 36 in which the coil 33 is situated,-to the pole piece 37 and then through the members 47 and 43 back to the left-hand pole of the magnet 45. The pole piece 37 recedes adjacent to the shank 39 of the core piece 35 to define an enlarged annular gap behind the annular gap in which the coil 33 is situated in order to concentrate the magnetic lines of force in the annular gap passing through the coil 33.

To fire the hammer and cause the blade 17 to strike toward the helical bar 13, a hammer firing pulse is applied to the coil 33 via leads 54. The polarity of the pulseis such that the current flowing'through the coil 33 creates a magnetic field which reacts with the magnetic flux in the annular gap to propel the coil 33 outwardly toward the drum 1 l. The action drives the blade 17 against the helicalbar 13 as the frame 23 pivots on pins 25. The energizing pulse is of very short duration; blade 17 strikes the paper 19 and pushes it against the bar 13 in free flight and rebounds back against a pair of resilient stops 48. Advantageously, the blade 17 is made of a material having a high permeability so that the magnetic field in the gap biases the hammer to rest against the stops 48.

One stop 48 is provided on each side of the frame 23 near the right hand and left hand end of the blade in order to minimize any tendency of the hammer blade to oscillate after it strikes the bar 13. This oscillation may cause the hammer to restrike the paper again lightly and cause what is known in the art as ghosting. However, it should be noted that in certain patterns, as where the hammer prints a dot in two successive positions, the hammer may not return to the stops before its again fired.

. It should be noted that since the blade 17 spans a number of character positions (eleven, for example) it must be stiff along its length so that its twist period is quite short. When the blade 17 strikes the helix 13 in any position except dead center on the blade 17, a twising moment is produced which incites a twisting transient oscillation about an axis perpendicular to the direction of motion of the blade. In'order to achieve a high quality and uniform definition of printed dots throughout the length of the printer blade, this twist period or transient oscillation must be kept to a minimum. This is achieved by providing a stiff, yet lightweight frame 23 for supporting the blade 17 and the two bumpers 48 located near the ends of the blade to absorb the twisting moment. The pivotal mounting structure comprising the pins 25 and the U-shaped bracket 27 defining a rigidly fixed pivot axis together with the stiff frame 23 inherently restrains the blade against the twisting moment applied to the blade when it strikes the helical bar offcenter.

As shown in the block diagram of FIG. 4, which illustrates the system for controlling the printer of the present invention, signals representing alphanumeric characters to be printed are received and stored in character' receiving storage 56. Each alphanumeric character embodiment one line of characters to be printed consists of 132 characters, so the one line buffer storage 53 stores 132 binary characters. In order to permit the printer to print alphanumeric charactersseparated by spaces, one binary character is selected to represent a space.

The drum 11, as shown in FIG. 4, drives two timing discs 55 and 57. Each time the drum 11 rotates through one revolution and comes to the start position in which the helical bar is shown in FIG. 4, the timing disc 55 will produce a reset pulse in a transducer 59 positioned to sense the timing disc 55. The timing disc 57 produces pulses in a transducer 61 as the drum 11 rotates. These pulses are produced at a rate of one pulse per horizontal dot position in the character fields as these dot positions come in position to be printed by the hammers 15. As will be apparent to those skilled in the art, a single timing disc with a missing'tooth to provide a reset pulse may be employed instead of the separate disc 55 and transducer 59.

As pointed out above, each hammer spans 1 1 character positions and each character field is five dot positions wide. Each character field is separated from the adjacent character field in the same line by two dot positions. Accordingly, in the preferred embodiment each hammer spans 77 horizontal dot positions and the timing disc 57 produces 77 evenly distributed pulses in the transducer 61 for each revolution of the drum l1. Pulses produced by the transducer 61 are applied to a series of five-bit shift registers 63, there being one shift register 63 for each hammer 15. Pulses from the transducer 61 are applied to the shift registers 63 only while the intersections of the helical bar 13 and the hammer blades 15 are passing through the dot positions of character fields. Pulses produced in the transducer 61 while the intersections between the helical bar 13 and the hammer blades 15 are between character fields are not applied to the shift registers 63 as will be explained in more detail below with reference to FIG. 5. At the start in the shift registers 63 so that the proper pattern of horizontal dots is printed by each hammer 15. Thus, the binary codes stored in the registers 63 represent horizontal row dot patterns of the alphanumeric character fields with each binary one representing a dot and each binary zero representing the absence of a dot.

While the helical bar and hammer blade intersections pass through the two dot positions between the first or left hand character field and the second character field to be printed by each hammer, the logic and control circuitry 65 again fills each five bit shift register 63 with five bit binary signals representing the top row dot pattern of the second character to be printed by the corresponding hammer. As the helical bar and hammer.

blade intersections then pass through the dot print positions of the top row of dots in the character field of the second character to be printed by each hammer, the transducer 61 will apply pulses to the shift registers 63 and cause the signals stored therein to be shifted out. Again, each time as a pulse is shifted out of a shift register 63 representing a binary one, a corresponding hammer 15 will be fired and will print a dot, and in this manner a correctpattern of dots is printed in the top row of dot positions in the character fields of the second character to be printed by each hammer.

In a similar manner, five bit binary codes are successively stored in the shift registers 63 to represent the patterns to be printed by each hammer in the top row of dot positions of each successive character field and the patterns are printed in succession. This process continues until the patterns in the top row of the character fields of the entire line of 132 characters has been of the operation of the printer to print a newline of print after a new line of characters has been stored in the buffer storage 53, logic and control'circuitry 65 will respond to the signals representing the first or left hand alphanumeric character to be printed by each of the hammers 15 and store in each of the shift registers 63 a selected five bit binary code. Then, as the registers 63 receive the pulses from the transducer 61, these pulses will cause the registers 63 to shift and serially produce a pulse for each binary l stored in the shift registers. Each time a shift register 63 produces a pulse, it is applied to a corresponding hammer driving circuit 67, which in response receiving such a pulse will apply a firing pulse to the coil of the corresponding hammer 15. As a result, the corresponding hammer 15, in response to each output pulse produced by shift register 63, will fire and will strike against the helical bar 13. The pulses produced by the transducer 61 are timed so that the corresponding hammer firing pulses produced in response thereto occur as the intersections between the helical bar 13 and the hammer blades 17 pass through the top row of dot positions of the first or left hand character field to be printed by each hammer. In this manner, the top horizontal row of dots in the first or left hand character field corresponding to each hammer is printed. The logic and control circuitry 65, responsive to the corresponding binary characters stored in the buffer storage 53, stores the proper binary codes printed. At this time the drum 11 will have completed one revolution and the timing disc 55 will cause the transducer 59 to produce a pulse which is applied to the logic and control circuitry 65. Because the web of paper on which the printing is carried out is continuously moving, the paper will have moved to the print position for the second row of dots for the first character field to be printed by each of the hammers 15 by the time thedrum has completed one revolution. As the drum rotates, the logic and control circuitry 65 will repeat the process of filling the five bit registers 63 with five bit codes corresponding to the dot patterns to be printed in the second row of dot positions in each character field. In selecting the proper codes to be stored in the shift registers 63, the logic and control circuitry 65 again responds to the six bit binary characters stored in the one line buffer storage 53. After the second row of dot positions has been printed, the third through seventh rows of dot positions in each character field is printed in a similar pattern so that an entire line of alphanumeric characters is printed corresponding to the binary characters stored in the one line buffer storage 53. When an entire line has been printed, the character receiving storage 56 then transmits binary characters representing the next line of alphanumeric characters to be printed to the one line buffer storage 53, whereupon the system prints the next row of alphanumeric characters in the same manner.

As shown in FIG. 5, the one line buffer storage 53 comprises a plurality of 66 bit shift registers 71, one for each of the hammers 15. Since in the preferred em bodiment there are twelve hammers 15, there are twelve shift registers 71. Each shift register 71 stores eleven six bit characters representing the eleven alphanumeric characters to be printed by the corresponding 7 hammerin the print lineon the paper web presently opposite the hammers. When shift pulses are applied toone of the shift registers 71, signals representing the first binary character stored in the shift register are shifted out of the front end of the register and also at the same time recirculated into the back end of the register as indicated by the channels 73. The shift registers 71 are filled with binary characters from the character receiving storage 56 by conventional circuitry not shown. When the shift registers 71 have been filled with a new line of binary characters so that the system is ready to print a new line of alphanumeric characters,

the character receiving storage 56 will apply a signal to a flipflop 75 to set the flipflop 75in the-state in which it enables a gate 77. The next pulse produced by the transducer 59 when the drum 11 gets to the start position will pass through the enabled gate 77 to set a flipflop 79 to a state in which it applies an enabling signal to a gate 81, which is connected to receive 250 kilocycle clock'pulses from a clock pulse generator 83. In order to pass the applied clock pulses, the gate 81 must also receive an enabling signal from a flipflop 85.

. The pulse produced by the transducer 59 in response to the drum 11 reaching the start position is also applied to a counter 87, a twelve bit ring counter 89, and to a counter 91 to set the counters 87 and 91 to zero and to set ring counter 89 to register a count of one. When the counter 87 is set to zero, it sets the flipflop 85 in a condition to apply an enabling signal to the gate 81. Thus, after the flipflop 75 has been set by asignal from the data receiving storage 51, the flipflops 79 and i 85 will be set when the next pulse is produced by the transducer 59 upon the drum 11 coming to its start position, and the gate 81 will be enabled. When the gate 81 is enabled, the clock pulses produced by the clock 83 will pass through the gate 81 and will be applied to a set of twelve AND gates 93, one for each shift register 71 and also to the counter 91 which will begin counting the 250 kilocycle clock pulses.

The 12 bit ring counter 89, having been set to register a count of one by the pulse produced by the transducer 59 upon the drum 11 passing through its start position, will enable the uppermost gate 93, whereupon the 250 kilocycle clock pulses will pass through this gate 93 to the shift input of the uppermost register 71, which corresponds to the first or left hand hammer of the printer. Output signal pulses representing binary data produced from the front end of any of the shift registers 71 are applied to a corresponding output gate 95.

When the 12 bit ring counter 89 enables a gate 93 at the input of a shift register 71, it will also enable a corresponding output gate 95. Thus, when the clock pulses are applied to the shift input of the uppermost register 71, binary data signal pulses shifted out of the front end of the shift register 71 will pass through a corresponding gate 95 at the output of the shift register and then through an OR gate 97 to a serial-to-parallel converter '99. The clock pulses passing through the gate 81 are also applied to ,the serial-to-paralle'l converter I 99 so that the output signal pulses shifted out of the front end of the uppermost shift register 71 are shifted into the is counted by the ring counter 89, which thereupon registers a count of two 'and'switches to enable the input and output gates 93 and 95, corresponding to the shift register 71 second from the top as shown in FIG. 5. Thus, only six bits consisting of the first binary character stored in the uppermost shift register 71 will be shifted out and into the serial-to-parallel converter 99.

Signals representing the binary character stored in the serial-to-parallel converter 99 are applied in parallel to a read only memory 101. The output pulse produced by the counter 91 is also applied to the read only memory 101, and in response to the applied pulse from the counter 91, the read only memory 101 will read out a five bit binary code from an address selected by the binary character in the serial-to-parallel converter 99 and by the count registered in row counter 103. When the data receiving storage applies a signal to the flipflop indicating that the shift registers 71 have been filled with binary characters representing alphanumeric characters to be printed in one row, it also applies a signal to the row counter 103 to set the counter 103'to zero. Then, when the next pulse is produced by the transducer 59, the row counter 103 will count this pulse. Thus, the counter 103 will contain a count of one when the counter 91 produces an output pulse after the signal pulses representing a binary character have been read out of the uppermost shift register 71 and stored in the serial-to-parallel converter 99. The read only memory 101 has stored at each storage address a binary code representing a dot pattern to be printed in a horizontal row. These dot patterns can be selected to compose each alphanumeric character. The binary code that is read out from the memory position selected by the binary number stored in the converter 99 and the count registered in the counter 103 will be a dot pattern corresponding to the alphanumeric character represented by the binary character in the converter 99. The dot pattern read out will also correspond to the row represented by the count registered by the counter 103. Thus, when the signals representing the first binary character have been read out of the uppermost shift register 71' and into the converter 99, the read only memory 101' in response to the pulse produced by the counter 91 will read out signals representing a dot pattern corresponding to the first row of the first character stored in the uppermost shift register 71.

The signals read out from the memory 101 are applied in parallel to a series of gates 105, one corresponding to each hammer 15. When the 12 bit ring counter 89 registers a count of one, it will enable the gate 105 corresponding to the first hammer and there fore corresponding to the uppermost shift register 71. As pointed out above, when the counter 91 produces an output pulse, the ring counter 89 will count the applied pulse and register a count to enable the gates 93 and corresponding to the shift register 71 second from the top as shown in FIG. 5. At this time the ring 9 shift register 63 corresponding to the first hammer. In this manner binary signals corresponding to the dot pattern of the first row of the character to be printed in the first or left hand character position is stored in the shift register 63 corresponding to the first hammer.

After signals representing the first character have been read out and stored in the converter 99 in response to the-first six clock pulses passing through the gate 81, as pointed out above the 12 bit counter 89 will enable the gates 93 and 95 corresponding to the shift register 71 second from the top. Accordingly, the next six pulses passing through the gate 81 will shift out signals representing the first character stored in the second shift register 71. These signals will pass through the corresponding output gate 95 and through the gate 97 to be stored in the serial-to-parallel converter 99. After the six signal bits have been read out of the second shift register 71, the counter 91 will again recycle to zero and produce an output pulse to cause the read only memory 101 to again read out signals representing a row dot pattern. Since the row counter 103 will still contain a count of one, the dot pattern will be that for the first row of the character presently in the serial-toparallel converter, which character has just been read out of the second shift register 71 from the top as shown in FIG. 5. Signals representing this clot pattern will be applied to the gates 105. The ring counter 89, which is advanced to a count-of three in response to the output pulse of the counter 91, will still register a count of two when these signals are read out of the read only memory 101 and accordingly the gate 105 corresponding to the second hammer will be enabled. Thus, the signals will pass through the enabled gate 105 and will be stored in the five bit shift register 63 corresponding to the second hammer of the printer. In this manner signals representing the dot pattern of the first row corresponding'to the first character in the second shift register 71 is stored in the five bit register 63 corresponding to' the second hammer.

Each time a six bit character is read out andstored in the serial-to-parallel converter 99 as described above, the twelve bit counter 89 advances to the next count so as to read a character out of tne next shift register and into the serial converter 99. Immediately after the character is read into the converter 99 as described above, the output pulse produced by the counter 91 causes a dot pattern to be stored in the appropriate shift register 63, and in this manner each of the five bit registers 63 is made to store a dot pattern corresponding to the first row of the first character in the corresponding 66 bit shift register 71. When the first character in the last shift register 71 is being read out and into the converter 99, the ring counter 89 in addition to enabling the input and output gates 93 and 95 of this shift register, will also enable a gate 111, which is connected to receive the output pulse produced by thecounter 91 when it recycles to zero. Accordingly, when the first character has been read out of the last shift register 71,

the pulse produced by the counter 91 will pass through the gate llland reset the flipflop 85 so that it no longer'enables the gate 81 and the clock pulses from the 250 kilocycle clock 83 will be stopped at the gate 81.

The counter 87, which is connected to count the pulses produced by the transducer 61, recycles to zero upon counting the next pulse after reaching a count of six. While the shift registers 63 were being filled with signals representing dot patterns as described above, the pulses produced by the transducer 61, in response to the timing wheel 57, are counted by the counter 87. Before the counter 87 can reach a count of two, all 12 of the shift registers 63 will have been filled with signals representing a row dot pattern as described above. When the counter 87 reaches a count of two. it will enable a gate 113 and it will continue to enable the gate 113 until the counter 87 recycles to zero after reaching a count of six, whereupon it will no longer enable the gate 113. The gate 113 is also connected to receive the pulses produced by the timing wheel 57 in the transducer 61 and when enabled will pass these pulses through to the shift registers 63. As a result. the four pulses produced by the transducer 61 while the counter 87 is counting from two to six will pass through the gate 1 13. The next pulse produced by the transducer 61 will cause the counter 87 to recycle to zero whereupon the gate 113 will no longer be enabled. This pulse which causes the counter 87 to recycle to zero also passes through the gate 113 because of the inherent delay in the counter 87 in recycling to zero. Thus a sequence of five pulses pass through the gate 113 to shift the signals representing the dot patterns in the shift registers out of the shift registers to the hammer driving circuits 67, and thus cause the dot patterns to be printed on the paper web. In this manner the dot pattern corresponding to the first row of the first character stored in each of the shift registers 71 is printed on the paper web. These characters will actually be printed the 1st, the 12th,the 23rd, the 34th, the 45th, the 56th, the 67th, the 78th, the 89th, the 100th, the 111th, and the 122nd character position in the print line.

As signals representing each of the binary characters are shifted out of the shift registers 71, these signals are recirculated into the back of the register so that when the first character has been shifted out of each of the registers, the first character will be stored at the back of the register and the second character in each of the shift registers will be at the front of the register. These characters will now be ready to be transferred into the converter 99.

When the dot pattern corresponding to the first row of the first character in each of the registers 71 has been printed and the seven bit counter 87 recycles to zero, the counter 87 will apply a signal to the flipflop to again set the flipflop to enable the gate 81. Accordingly, clock pulses from the source 83 will again pass through the gate 81 to the gates 93, the counter 91, and the converter 99. The output pulse produced by the counter 91 which reset the flipflop 85 so that the gate 81 was no longer enabled, also recycled the ring counter 89-to again register a count of one so that the ring counter again enables the input and output gates 93 and 95 and the gate corresponding to the uppermost shift register and corresponding to the first hammer. The system then operates in a manner similar to that described above to fill up theshift registers 63 with signals representing row dot patterns corresponding to the second character stored in each of the shift registers 71. These dot patterns will still be first row dot patterns since the row counter 103 will still contain a count of one. While the registers 63 are still being filled in this manner, the counter 87 will be counting the output pulses produced by the transducer 61 and the filling of the registers 63 will be completed before the counter 87 reaches a count of two. When the counter 87 reaches a count of two, the gate 113 will again be enabled by the counter 87 and the next five pulses produced by the transducer 61 will pass through the gate 113 and shift out the row dot patterns stored in the registers 63 and cause these patterns to be printed on the paper web. Thesepatterns will be printed in the 2nd, 13th, 24th, 35th, 46th, 57th, 68th, 79th, 90th, 101st, 112th, and 123rd character positions in the print line. These patterns will be printed in these positions because the helical bar 13 will be opposite these character positions as the patterns are read out of the registers 63. This relationship necessarily occurs because the shift pulses which cause the registers 63 to be read out are the tenth through thirteenth pulses produced by the transducer 61 after the drum 11 passes through'the start position, the seven bit counter 87 having recycled once and reached a count of two before these particular dot patterns are read out of the shift registers 63. The pulse that causes the last dot position of the patterns stored in the shift registers 63 to be read out also causes the sevenbit counter. 87 to again recycle to zero so that the gate 113 is again no longer enabled. At this time, in the same manner as described above, the third character stored in each of the registers 71 is read out in sequence to the serial-to-parallel converter 99 and in response thereto, row dot patterns are read out of the read only memory 101 and stored in the shift registers 63. Since the row counter 103 still contains a count of one, these row dot patterns are all the patterns for the first row of the characters which are read out of the shift registers 71 to the converter 99. The row dot patterns are then again shifted out from the shift registers 63 in the same .manner as described above and are printed on the paper web. In thismanner the first row dot patterns for the third character corresponding to each hammer is printed. In a similar manner thereniaining characters stored in each of the registers 71 are read and the corresponding row dot pattern is printed by the hammer for each character. When all the characters have been read out of the shift registers and row dot patterns corresponding to each pattern have been printed, the printer will have printed the top row dot pattern for each of the 132 characters to be printed. Immediately after the lastrow dot pattern has been printed and before the next pulse is produced by the transducer 61, the drum 11 will come into its start position and cause the transducer 59 to produce an output pulse which is applied to therow counter 103 to increase the count. therein to two. At this point thecounter 87 should contain a count of zero, the 12 bit ring counter 89 should contain a count of one, and the counter 91 should contain a count of zero. In case any of these counters should not contain these counts due to malfunction, the output pulse of the transducer 59 is applied to these counters to set the counters 87 and 91 to zero, and to set the count of the counter 89 to one. Also at this time, the characters stored in each of the registers 71 will have been completely recirculated since the last character will have been readout of each of the registers and shifted into the back end of the register. Accordingly, at this time the first character stored in each register 71 again will be at the front end of such register.

The process repeats just as described above except that this time the dot patterns which are stored in the registers 63 and printed by the printer correspond to the second row of dotpattems of the characters stored in the registers 71 rather than the first row of dot patterns because the row counter 103 will contain a count of two. Because the paper web is moving as the process is being carried out, these rows will be printed by the printer directly beneath the first rows. In a similar manner the third through seventh row dot patterns are printed for each character as the counter 103 counts to seven. Upon reaching a count of seven, the next pulse produced by the transducer 59 causes the row counter 103 to recycle to a count ofone when the drum 1] again comes into the start position. Upon recycling to one, the row counter 103 produces an output pulse which resets the flipflop 79 causing it to remove the enabling signal from the gate 81 so that no further clock pulses can be transmitted through the gate 81. In addition, this signal is transmitted to the character receiving storage to indicate that the line of characters has been printed and that the one line storage comprising the registers 71 is ready to receive a new line of characters. In this manner the printer prints a line of alphanumeric characters corresponding to the binary characters stored in the shift registers 71.

As point out above, the transducer 61 produces a pulse each time the intersection of the helical bar 13 and the hammer blades pass through a dot position in the print line. However, no dots are printed while those pulses are produced which cause the counter 87 to count from zero to two when the shift registers 63 are being filled. The omission of any printed dots from the corresponding dot positions while the counter 87 is counting from zero to two provides the spaces between the characters. The output signal of the row counter 103 also resets the flipflop so that it no longer enables the. gate 77. The system is then ready to print a new line of characters and upon receiving a signal from the character receiving storage that the shift registers 71 have been refilled with a new line of characters, which signal again sets the flipflop 75, the system will print a new line of characters just as described above.

, The above described helical bar printer, because of the logical. system for controlling the actuation of the hammers and because of the unique hammer construction, is able to print alphanumeric characters in response to binary input characters at a very high speed and therefore can be used effectively to print the output from computers and data processing equipment. In addition, it should be noted that certain aspects and subcombinations of the invention may be utilized independently. For example, the printer may be advantageously employed for facsimile printing in which case the printer logic may be modified. The above description is of a preferred embodiment of the invention and many modifications may be made thereto without departing from the spirit and scope of the invention, which is defined in the appended claims.

What is claimed is:

1. A printer comprising a bar formed in a helix, means to'rotate said bar about the axis of said helix, at least one hammer positioned to strike'said bar as said bar rotates, said hammer having a striking edge that extends along a print line and spans a convolution of said helix, means mounting said hammer for movement of said striking edge in a predetermined path to strike said bar to print a dot while rigidly restraining said striking edge from twisting about any axis perpendicular to the direction of movement of said striking edge in said predetermined path, a coil of electrically conducting wire affixed to said hammer, means for generating a magnetic field which passes through said coil, said coil being supported so that it is free to move relative to said field and to drive said hammer against said bar, said hammer including means urging said hammer away from said helix when said coil is not energized, a portion of said hammer adjacent to said coil being made from a material having a high permeability, said urging means being the force of attraction between the field generated by said permanent magnet and said hammer portion, and means to apply firing pulses to said coil to drive said striking edge against said bar to print a dot for each applied firing pulse.

2. A high speed printer comprising a bar formed into a helix, means to rotate said bar about the axis of said helix, at least'one hammer comprising a rigid frame, and a blade mounted on said frame, means pivotally mounting said frame on a pivot axis rigidly fixed with respect to and extending generally parallel to the axis of said helix, said blade being spaced from said pivot axis and having an edge extending generally parallel to the axis of said helix and positioned adjacent to said bar so as to be able to strike said bar by pivoting about said pivot axis, a coil of electrically conducting wire fixed to said blade, ing radially through said coil, said coil being supported so that it is free to move relative to said field and drive said blade against said bar, and means to apply firing pulses to said coil to drive said blade against said bar to print a dot for each applied firing pulse.

3. A printer comprising a print member, at least one hammer positioned adjacent to said print member and movable to strike said member to carry out printing, an electrically conducting coil fixed to said hammer, means defining a gap and for generating a magnetic field passing through said gap, said coil being positioned in said magnetic field in said gap free from the surfaces defining said gap, a portion of said hammer adjacent to said gap being-of a material having a high permeability whereby said magnetic field at said gap urges said hammer away from said print member, and means to apply firing pulses to said coil to drive said hammer means for generating a magnetic field passagainst said print member to print a predetermined figure for each applied firing pulse.

4. A printer comprising a bar formed in a helix, means to rotate said bar about the axis of said helix, at least one hammer positioned to strike said bar as said bar rotates, said hammer comprising a rigid frame rigidly supporting a striking blade having a striking edge that extends along a print line and spans a convolution of said helix, means pivotally mounting said frame about a pivot axis rigidly fixed with respect to the axis of said helix for movement of said striking edge in a predetermined path to strike said bar to print a dot while rigidly restraining said striking edge from twisting about any axis perpendicular to the direction of movement of said striking edge in said predetermined path, a coil of electrically conducting wire affixed to said striking blade, means for generating a magnetic field which passes through said coil, said coil being supported so that it is free to move relative to said field and drive said hammer against said bar, and means to apply firing pulses to said coil to drive said striking edge against said bar to print a dot for each applied firing pulse.

5. A printer as recited in claim 4 further comprising means to receive binary coded signals representing alphanumeric characters, and logic means responsive to said binary coded signals to control the application of said firing pulses to said coil to print dots in patterns to compose the alphanumeric characters represented by said binary coded signals in'a plurality of character positions along said print line, said hammer blade extending along said print line through a plurality of said character positions.

6. A printer as received in claim 4 further including means located adjacent each end of said striking edge to dampen oscillation of the hammer.

7. A printer as in claim 4 wherein said means for generating a magnetic field comprises a permanent magnet and a core within said coil and a pole piece substantially surrounding said coil in order to concentrate the field produced by said magnet across said coil.

8. A printer as recited in claim 7 wherein said hammer includes means urging said printer away from said helix when said coil is not energized. 

1. A printer comprising a bar formed in a helix, means to rotate said bar about the axis of said helix, at least one hammer positioned to strike said bar as said bar rotates, said hammer having a striking edge that extends along a print line and spans a convolution of said helix, means mounting said hammer for movement of said striking edge in a predetermined path to strike said bar to print a dot while rigidly restraining said striking edge from twistiNg about any axis perpendicular to the direction of movement of said striking edge in said predetermined path, a coil of electrically conducting wire affixed to said hammer, means for generating a magnetic field which passes through said coil, said coil being supported so that it is free to move relative to said field and to drive said hammer against said bar, said hammer including means urging said hammer away from said helix when said coil is not energized, a portion of said hammer adjacent to said coil being made from a material having a high permeability, said urging means being the force of attraction between the field generated by said permanent magnet and said hammer portion, and means to apply firing pulses to said coil to drive said striking edge against said bar to print a dot for each applied firing pulse.
 2. A high speed printer comprising a bar formed into a helix, means to rotate said bar about the axis of said helix, at least one hammer comprising a rigid frame, and a blade mounted on said frame, means pivotally mounting said frame on a pivot axis rigidly fixed with respect to and extending generally parallel to the axis of said helix, said blade being spaced from said pivot axis and having an edge extending generally parallel to the axis of said helix and positioned adjacent to said bar so as to be able to strike said bar by pivoting about said pivot axis, a coil of electrically conducting wire fixed to said blade, means for generating a magnetic field passing radially through said coil, said coil being supported so that it is free to move relative to said field and drive said blade against said bar, and means to apply firing pulses to said coil to drive said blade against said bar to print a dot for each applied firing pulse.
 3. A printer comprising a print member, at least one hammer positioned adjacent to said print member and movable to strike said member to carry out printing, an electrically conducting coil fixed to said hammer, means defining a gap and for generating a magnetic field passing through said gap, said coil being positioned in said magnetic field in said gap free from the surfaces defining said gap, a portion of said hammer adjacent to said gap being of a material having a high permeability whereby said magnetic field at said gap urges said hammer away from said print member, and means to apply firing pulses to said coil to drive said hammer against said print member to print a predetermined figure for each applied firing pulse.
 4. A printer comprising a bar formed in a helix, means to rotate said bar about the axis of said helix, at least one hammer positioned to strike said bar as said bar rotates, said hammer comprising a rigid frame rigidly supporting a striking blade having a striking edge that extends along a print line and spans a convolution of said helix, means pivotally mounting said frame about a pivot axis rigidly fixed with respect to the axis of said helix for movement of said striking edge in a predetermined path to strike said bar to print a dot while rigidly restraining said striking edge from twisting about any axis perpendicular to the direction of movement of said striking edge in said predetermined path, a coil of electrically conducting wire affixed to said striking blade, means for generating a magnetic field which passes through said coil, said coil being supported so that it is free to move relative to said field and drive said hammer against said bar, and means to apply firing pulses to said coil to drive said striking edge against said bar to print a dot for each applied firing pulse.
 5. A printer as recited in claim 4 further comprising means to receive binary coded signals representing alphanumeric characters, and logic means responsive to said binary coded signals to control the application of said firing pulses to said coil to print dots in patterns to compose the alphanumeric characters represented by said binary coded signals in a plurality of character positions along said print line, said hammeR blade extending along said print line through a plurality of said character positions.
 6. A printer as received in claim 4 further including means located adjacent each end of said striking edge to dampen oscillation of the hammer.
 7. A printer as in claim 4 wherein said means for generating a magnetic field comprises a permanent magnet and a core within said coil and a pole piece substantially surrounding said coil in order to concentrate the field produced by said magnet across said coil.
 8. A printer as recited in claim 7 wherein said hammer includes means urging said printer away from said helix when said coil is not energized. 